Hydrogenation method for unsaturated block copolymers and hydrogenated unsaturated block copolymers

ABSTRACT

Use is made, for selectively hydrogenating the olefinic double bonds of block copolymers, at least one block of which comprises olefinic double bonds, using a catalyst based on a metal from Group VIII in a medium comprising an organic solvent for the copolymer and an ionic liquid as solvent for the catalyst, of a water-immiscible ionic liquid, preferably an ionic liquid for which the anion is the hexafluorophosphate anion and the cation is the 1-butyl-3-methylimidazolium (bmim + ) or 1-ethyl-3-methylimidazolium (emim + ) cation. 
     Applied to poly(styrene)-b-poly(butadiene)-b-poly(methyl methacrylate) block copolymers, the poly(butadiene) block of which predominantly possesses a 1,4-microstructure, this process results in copolymers for which the degree of hydrogenation is at least equal to 50% and which exhibit a melting point of greater than 30 °C.

FIELD OF THE INVENTION

The present invention relates to the field of block copolymers and hasmore particularly as subject-matter a process for the hydrogenation ofunsaturated block copolymers and novel hydrogenated block copolymers.

BACKGROUND OF THE INVENTION

AB or ABC block copolymers having at least one block comprising olefinicdouble bonds (polybutadiene, polyisoprene, and the like) can be usedalone or as a blend with other polymers, such as PVDF, PVC, PVCC, andthe like, for improving some of their properties. However, the presenceof the block comprising olefinic double bonds renders them sensitive tolight, to some oxidizing agents and to heat. The selective hydrogenationof this block makes it possible to prepare novel materials comprisingpolyolefins while improving their stability (towards light, towardsoxidizing agents and towards heat) and their mechanical properties. Thishydrogenation also results in a modification in the physical propertiesof the polymer by creating a block comprising fewer olefinic doublebonds, which block can become a semicrystalline block. Furthermore, thepresence of a polyolefin chain renders them compatible with a broaderrange of polymers (including polyolefins), which represents a very largepotential market.

The hydrogenation of these block copolymers can be carried out bynon-catalytic methods, generally performed in the presence of hydrazinederivatives, such as, for example, p-toluenesulphonylhydrazine. Althoughthese methods do not require a reactant which operates under pressure,their industrial implementation cannot be envisaged because of the highcost of the p-toluenesulphonylhydrazine reactant.

Block copolymers can also be hydrogenated by heterogeneous catalysis.However, as heterogeneous catalysts have a low activity, it is necessaryto operate at a high temperature and a high hydrogen pressure and to uselarge amounts of catalyst. These operating conditions can result in adecomposition or in a crosslinking of the polymer and in a decrease inthe selectivity of the hydrogenation (hydrogenation of functional groupsother than the olefinic double bonds: esters, aromatic double bonds, andthe like).

The hydrogenation can also be carried out in a homogeneous medium undermilder conditions by using, as catalysts, noble metal complexes(Wilkinson's catalyst, and the like) or cobalt or nickel salts withreducing agents (triethylaluminium, butyllithium, and the like). The useof a very small amount of catalyst can result in an economical process,even if the catalyst is not recovered; however, the latter partlyremains in the polymer, which can be harmful to its properties and thusrequire its purification. On the other hand, when it is necessary to usea large amount of catalyst, it has to be recovered for recycling.

The hydrogenation of block copolymers having a polybutadiene block byhomogeneous catalysis in the presence of Wilkinson's catalyst has formedthe subject of many publications, in particular Patent Application DE 4240 445, the thesis by C. Auschra at the University of Mainz (1992),entitled “Synthese von neuartigen Multi block copolymer en und derenVerwendung in Polymerlegierungen” [Synthesis of novel multiblockcopolymers and their use in polymer alloys], the articles by C. Auschraet al. in Polymer Bulletin, 30 (1993), 257–264 and 305–311 and inMacromolecules, 26 (1993), 2171–2174, and an article by R. Stadler etal. in Macromolecules, 28 (1995), 3080–3097. The copolymers used have apolybutadiene block formed of butadiene predominantly possessing a1,2-microstructure (approximately 90%), which hydrogenates much moreeasily than polybutadiene predominantly possessing a 1,4-microstructure(85 to 89%). Furthermore, the amount of Wilkinson's catalyst used ishigh (8 000 molar ppm per mole of double bond).

The hydrogenation of a polystyrene-polybutadiene-poly(ε-caprolactone)triblock copolymer in the presence of Wilkinson's catalyst (10 000 ppm),the polybutadiene block predominantly possessing a 1,4-microstructure,is disclosed in Patent Application DE 19643889 and in Macromol. Chem.Phys., 199 (1998), 1063–1070.

The selective hydrogenation of the polybutadiene block of an NBR(Nitrile Butadiene Rubber) copolymer without affecting the nitrilegroups is described by L. A. Müller et al. in Macromol. Rapid Commun.,19 (1998), 409–411. The reaction, catalysed by the RuHCl(CO)(PCy₃)₂complex, is carried out in a two-phase medium (ionic liquid+organicsolvent); the ionic liquid is 1-butyl-3-methylimidazoliumtetrafluoroborate (bmimBF₄) and the NBR is dissolved in toluene. Theionic liquid solution comprising the catalyst can be recycled severaltimes.

This process, which makes it possible to easily recover the catalyst andto recycle it, also forms the subject-matter of Patent Application BR 9802101, Example 2 of which illustrates the same hydrogenation of an NBRwith the same ionic liquid (bmimBF₄) but the general features of whichinclude a good number of other catalysts, of other unsaturatedcopolymers and of other ionic liquids, such as those in which the cationis a quaternary ammonium or phosphonium group and the anion derives froma Lewis acid, such as, for example, the AlCl₄ ⁻, RSO₃ ⁻, BF₄ ⁻, ZnCl₄²⁻, ZnBr₄ ²⁻, PF₆ ⁻, CuCl₂ ⁻ or FeCl₃ ⁻ anions, and the like.

As indicated above, the hydrogenation of copolymers comprising abutadiene block predominantly possessing a 1,4-microstructure isdifficult. Thus, when the method of Example 2 of document BR 98 02101 isapplied to the hydrogenation of such a copolymer (SBM triblock) withWilkinson's catalyst at a moderate temperature (60° C.), a degree ofhydrogenation of the order of 30% only is obtained.

DESCRIPTION OF INVENTION

It has now been found that this degree is greatly improved by using awater-immiscible ionic liquid, in particular an ionic liquid for whichthe anion is the hexafluorophosphate anion (PF₆ ⁻). Under the sameoperating conditions, the degree of hydrogenation changes from 30% to ofthe order of 75% by using 1-butyl-3-methylimidazoliumhexafluorophosphate (bmimPF₆) as ionic liquid.

This result is surprising as, in an article relating to thehydrogenation of cyclohexene in a two-phase medium with rhodiumcatalysts dissolved in ionic liquids of the bmim type [Polyhedron, 15,No. 7 (1996), 1217–1219], P. A. Z. Suarez et al. did not observe anysubstantial difference according to the nature of the anion: AlCl₄ ⁻,BF₄ ⁻ or PF₆ ⁻ (entries 2, 3 and 5 in Table 1).

A subject-matter of the invention is thus a process for the selectivehydrogenation of the olefinic double bonds of block copolymers, at leastone block of which comprises olefinic double bonds, using a catalystbased on a metal from Group VIII in a medium comprising an organicsolvent and an ionic liquid, characterized in that a water-immiscibleionic liquid is used.

The term “ionic liquid” is understood to mean here any non-aqueous saltwith an ionic nature which is molten at ambient temperature or at leastat moderate temperature (<150° C.). In these ionic liquids, which can berepresented by the general formula Q⁺A⁻, Q⁺ is a quaternary ammonium,aromatic ammonium, quaternary phosphonium or ternary sulphonium cation.

The anion A⁻ of the ionic liquid according to the invention ispreferably the hexafluorophosphate anion. Mention may be made, asanother non-limiting example of A⁻ anions in accordance with theinvention, of the (CF₃SO₂)₂N⁻ anion.

Although it is preferable to use ionic liquids for which the cation isan imidazolium cation of general formula:

in which X¹ and X³, which are identical or different, are C₁–C₄ alkylradicals and X² is a hydrogen atom or a methyl radical, preferably a1,3-dialkylimidazolium cation and more particularly the1-butyl-3-methylimidazolium (bmim⁺) and 1-ethyl-3-methylimidazolium(emim⁺) cations, it would not be departing from the scope of the presentinvention to use an ionic liquid for which the Q⁺ cation corresponds toone of the following general formulae:R¹R²R³R⁴N⁺R¹R²R³R⁴P⁺R¹R²R³S⁺in which the R¹ to R⁴ symbols, which are identical or different, eachdenote a saturated or unsaturated, cyclic or non-cyclic, or aromatichydrocarbyl, chlorohydrocarbyl, fluorohydrocarbyl,chlorofluorohydrocarbyl or fluorocarbyl group having from 1 to 10 carbonatoms, it also being possible for one or more of these groups tocomprise one or more heteroatoms, such as N, P, S or O.

The ammonium, phosphonium or sulphonium cation Q⁺ can also form part ofa saturated or unsaturated or aromatic heterocycle having from 1 to 3nitrogen, phosphorus or sulphur atoms, it being possible for thisheterocycle to carry R¹ to R⁴ groups as defined above.

In the process according to the invention, the catalyst is dissolved inthe ionic liquid and the copolymer to be hydrogenated in an organicsolvent.

The catalyst used, based on a metal from Group VIII (in particularrhodium, ruthenium or palladium), is introduced in the form of a complexwhich is soluble in the ionic liquid. Mention may be made, asnon-limiting examples of such complexes, of Wilkinson's catalystRhCl(PPh₃)₃, Osborn's catalyst [Rh(nbd)(PPh₃)₂ ⁺PF₆ ⁻ and the complexesRuCl₂(PPh₃)₃ and PdCl₂(PPh₃)₂, Ph denoting the phenyl radical and nbddenoting norbornadiene. An excess of ligand (for exampletriphenylphosphine PPh₃, in the case of Wilkinson's catalyst) can beadded to the reaction mixture to prevent the complex from dissociating.

The organic solvent used to dissolve the copolymer to be hydrogenated ispreferably an aromatic solvent, such as benzene, toluene, xylene andethylbenzene. For economical reasons, the concentration of the copolymerin the organic solvent is preferably as high as possible. However, thisconcentration must be less than or equal to the solubility of thehydrogenated copolymer at the reaction temperature. Depending upon thecopolymer, this concentration can be between 3 and 60% by mass,preferably between 3 and 30% and more particularly between 3 and 15%.

Use may be made of between 0.01 and 5 molar % of catalyst per mole ofolefinic double bonds to be hydrogenated and preferably of between 0.02and 2 molar %.

The minimum amount of ionic liquid to be used depends on the catalystchosen and on its solubility in the ionic liquid. Thus, it is necessaryto introduce at least the volume of ionic liquid which makes it possibleto dissolve all the catalyst.

The ratio of the volume of ionic liquid to the volume of organic solventmust be between 0.01 and 25, preferably between 0.05 and 5 and moreparticularly between 0.1 and 1.

The hydrogenation according to the invention can be carried out atbetween 20 and 180° C., preferably between 20 and 150° C. and moreparticularly between 50 and 125° C. As the ionic liquid makes itpossible to stabilize the catalyst, it is possible to operate at highertemperatures than those used in homogeneous hydrogenation without anionic liquid and thus to accelerate the reaction rate. It is preferableto add a stabilizing agent for the polymer (0.1 to 5% by mass, dependingon the stabilizing agent), it being possible for the polymer todecompose if the temperature is too high.

The reaction can be carried out under a pressure of between 1 and 200bar relative, preferably between 1 and 100 bar and more particularlybetween 20 and 60 bar.

In order to obtain good dispersion of the hydrogen in the reactionmedium, it is advantageous to operate with efficient stirring, forexample by using, for this purpose, a Rushton auto-suction turbine.

After the reaction, the hydrogenated copolymer can be isolated byprecipitation, by introducing the reaction medium into a large amount ofa non-solvent for the hydrogenated copolymer (preferably an alcohol,such as methanol, ethanol or isopropanol), or, when there are twoseparate phases, by separation by settling of the organic phase and thenisolation of the copolymer according to the usual methods (for example,evaporation of the solvent or atomization or devolatilization orflocculation or precipitation from a non-solvent).

When the reaction medium does not separate by settling (first case), theprecipitation of the hydrogenated copolymer is carried out by using anon-solvent (preferably an alcohol) in an amount which can range from 1to 20 times the volume of the organic solvent and decreases inproportion as the degree of hydrogenation of the copolymer increases.Use is advantageously made of an amount of non-solvent ranging from 2 to10 times the volume of the organic solvent, preferably 5 to 10 times.The reaction medium comprising the hydrogenated copolymer is brought toa temperature of between 20 and 80° C., preferably between 25 and 60°C., and is then run into the non-solvent with stirring. The temperatureof the non-solvent before the reaction medium is run into it isadvantageously between 0 and 60° C., preferably 0 to 40° C. After thereaction medium has been run into the non-solvent, the stirring can bemaintained and the hydrogenated copolymer is then filtered off and thendried under vacuum. When the polymer is not completely hydrogenated, itis preferable not to heat it during the drying, so as to eliminate anyrisk of damage to the polymer (crosslinking, and the like). Thehydrogenated copolymer can be analysed by NMR and its remaining doublebonds can be quantitatively determined by measuring the bromine number.

The recycling of the catalyst can be carried out in two ways, dependingupon the method of isolation of the hydrogenated copolymer:

1. In the case where the ionic liquid phase was separated by settling,it is recycled directly to the reactor with the catalyst which itcomprises.

2. When the reaction mixture does not separate by settling, thehydrogenated copolymer is isolated by precipitation by introduction ofthe reaction mixture into a non-solvent. The filtrates obtained afterisolation of the copolymer are concentrated by evaporation of thenon-solvent and of a portion of the organic solvent, this evaporationpreferably being carried out at between 60 and 100° C. under reducedpressure. The concentrated solution, which then comprises the ionicliquid and the catalytic complex, which are not volatile, has added toit an amount of organic solvent equal to that lost during theevaporation and a fresh charge of copolymer for carrying out a freshhydrogenation.

The process according to the invention can be applied to thehydrogenation of any block copolymer with at least one block comprisingolefinic double bonds but it is of particular advantage for thehydrogenation of block copolymers of the SBM[poly(styrene)-b-poly(butadiene)-b-poly(methyl methacrylate)] type, thepoly(butadiene) block of which predominantly possesses a1,4-microstructure.

In these SBM copolymers, which are usually prepared by anionicpolymerization according to known methods, such as disclosed, forexample, in Patents EP 524 054 and EP 749 987, the percentage by mass ofthe poly(styrene) block can range from 5 to 80 (preferably from 10 to60), that of the poly(butadiene) block from 5 to 80 (preferably from 10to 60) and that of the poly(methyl methacrylate) block from 90 to 15(preferably from 80 to 30). Their number-average molar mass is generallyat least equal to 20 000 g/mol and preferably between 50 000 and 200 000g/mol. These copolymers can comprise synthetic intermediates, inparticular poly(styrene) and poly(styrene)-b-poly(butadiene) diblockcopolymer.

The application of the process according to the invention to theselective hydrogenation of these SBM copolymers makes it possible toobtain novel partially or completely hydrogenated block copolymers, thedegree of hydrogenation being at least equal to 50%, preferably between70 and 100% and more particularly between 90 and 100%. These novelcopolymers are crystalline at ambient temperature; they generallyexhibit a melting point of greater than 30° C.

EXAMPLES

In the following examples, which illustrate the invention withoutlimiting it, three SBM triblock copolymers and an SBS triblockcopolymer, defined below, were hydrogenated:

-   SBM-1: poly(styrene)-b-poly(butadiene)-b-poly(methyl methacrylate)    triblock copolymer with the composition (% by mass) 34/35/31, the    average molar mass of the poly(styrene) block being 27 600 g/mol and    89% of the poly(butadiene) block possessing a 1,4-microstructure.-   SBM-2: poly(styrene)-b-poly(butadiene)-b-poly(methyl methacrylate)    triblock copolymer with the composition (% by mass) 39/39/22, the    average molar mass of the poly(styrene) block being 36 700 g/mol and    89% of the poly(butadiene) block possessing a 1,4-microstructure.-   SBM-3: poly(styrene)-b-poly(butadiene)-b-poly(methyl methacrylate)    triblock copolymer with the composition (% by mass) 21/21/58, the    average molar mass of the poly(styrene) block being 15 900 g/mol and    88% of the poly(butadiene) block possessing a 1,4-microstructure.-   SBS: poly(styrene)-b-poly(butadiene)-b-poly(styrene) triblock    copolymer comprising 19 molar % of polystyrene and 81 molar % of    polybutadiene and 86% of the poly(butadiene) block possessing a    1,4-microstructure.

Example 1

A solution of 1.759 g of SBM-1 triblock copolymer in 33.25 g ofethylbenzene and a solution of 15 mg of Wilkinson's catalystRhCl[P(C₆H₅)₃]₃ and of 151.3 mg of triphenylphosphine (TPP) in 15.2 g of1-butyl-3-methylimidazolium hexafluorophosphate (ionic liquid bmimPF₆)are prepared in a glove box under a nitrogen atmosphere.

These two solutions are subsequently mixed with air excluded and thenthe two-phase mixture is introduced into a stainless steel autoclaveprovided with a PTFE internal lining and stirred by a Rushton turbine(stainless steel auto-suction turbine).

After confirming the leaktightness with nitrogen at 50 bar, the reactoris pressurized with 50 bar of hydrogen and the temperature is brought to60° C. for 24 hours with stirring (1 000 rev/min).

After cooling the reactor, 45 mg of Irganox® B900 (stabilizing agent)are added and the reaction mixture obtained (stable emulsion of lowfluidity) is then heated to 40° C. and then run into 350 ml of methanolat 40° C. with stirring. A white precipitate (hydrogenated SBM) and asingle clear liquid phase are obtained.

After filtering on a Büchner funnel and drying in a vacuum oven for 12hours at 25° C., 1.75 g of hydrogenated SBM and 377 g of clear filtratesare obtained. Quantitative determination of the remaining double bonds,carried out by measuring the bromine number and by NMR, indicates thatthe degree of hydrogenation of the polybutadiene block is 76%.

Analysis of the hydrogenated SBM shows a rhodium content of 10 ppm, i.e.a loss of 0.16 mg of Wilkinson's catalyst, which corresponds to 1% ofthe catalyst charged.

DSC analysis of the hydrogenated product shows a melting point of 54° C.(accuracy: ±2° C.), whereas the starting material (SBM-1) is notcrystalline.

Example 2

The filtrates from Example 1 (377 g) are concentrated on a rotaryevaporator at 90° C. under reduced pressure to remove the methanol.

1.750 g of SBM-1 triblock copolymer are dissolved in the concentratedsolution, positioned with air excluded, and then ethylbenzene is addedto bring the volume of the solution to 50 ml.

This solution is then charged to the autoclave and the hydrogenation iscarried out under the same conditions as in Example 1.

1.70 g of hydrogenated SBM are thus obtained with a degree ofhydrogenation of 66% and a rhodium content of 18 ppm.

Example 3 (Comparative)

The hydrogenation is carried out in the same equipment and according tothe same procedure as in Example 1 but without using an ionic liquid.

15 mg of Wilkinson's catalyst and 150 mg of TPP are dissolved in asolution composed of 1.759 g of SBM-1 and of 48.5 g of ethylbenzene. Thehydrogenation is carried out for 24 hours at 60° C. under a pressure of50 bar of hydrogen.

After precipitating from methanol, 1.58 g of SBM are obtained, which SBMis 75% hydrogenated and has a rhodium content of 290 ppm. Thiscorresponds to a loss of 4.13 mg of Wilkinson's catalyst, i.e. a loss 29times greater than that in Example 1 according to the invention.

Example 4

The hydrogenation is carried out as in Example 1, except that thestabilizing agent (45 mg of Irganox® B900) is added before the reactionto the SBM solution (1.754 g of SBM-1 and 33.45 g of ethylbenzene) andexcept that the hydrogenation reaction is carried out at 120° C. for 24hours under 50 bar of hydrogen.

At the end of the reaction, an emulsion is obtained which forms a gel,to which 100 ml of ethylbenzene are added, and heating is carried out at40° C. to liquefy the gel. The emulsion is subsequently run into 350 mlof methanol at 40° C. with stirring and then the white precipitateobtained is filtered off and dried as in Example 1.

1.75 g of SBM are obtained, which SBM is 97% hydrogenated and comprises26 ppm of rhodium, corresponding to 0.42 mg of Wilkinson's catalyst.

Example 5

The filtrates from Example 4 are concentrated on a rotary evaporator at90° C. under reduced pressure to remove the methanol.

1.754 g of SBM-1 copolymer are dissolved in the concentrated solution,positioned with air excluded, and then ethylbenzene is added to bringthe volume of the solution to 50 ml.

This solution is then charged to the autoclave and the hydrogenation iscarried out as in Example 4.

1.68 g of hydrogenated SBM are thus obtained with a degree ofhydrogenation of 95%.

Example 6

The hydrogenation is carried out exactly as in Example 4 but replacingthe Wilkinson's catalyst, which comprises rhodium, with 15.2 mg ofruthenium catalyst RuCl₂[P(C₆H₅)₃]₃.

1.75 g of hydrogenated SBM are obtained with a degree of hydrogenationof 89% and a ruthenium content of 1 ppm.

Example 7 (Comparative)

The hydrogenation is carried out in the same equipment and according tothe same procedure as in Example 6 but without using an ionic liquid.

15.3 mg of RuCl₂[P(C₆H₅)₃]₃ catalyst and 150 mg of TPP are dissolved ina solution composed of 1.755 g of SBM-1 and of 48.5 g of ethylbenzene.The hydrogenation is carried out for 24 hours at 120° C. under apressure of 50 bar of hydrogen.

After precipitating from methanol, 1.53 g of SBM are obtained, which SBMis 87% hydrogenated and has a ruthenium content of 60 ppm. Thiscorresponds to a loss of 0.87 mg of catalyst, i.e. a loss 60 timesgreater than that in Example 6 according to the invention.

Example 8 (Comparative)

The hydrogenation is carried out in the same equipment and according tothe same procedure as in Example 1 but using 1-butyl-3-methylimidazoliumtetrafluoroborate (bmimBF₄) as ionic liquid.

15 mg of Wilkinson's catalyst and 150 mg of TPP are dissolved in 15.1 gof bmimBF₄ and a solution composed of 1.757 g of SBM-1 and 33.23 g ofethylbenzene is added.

The hydrogenation is carried out for 24 hours at 60° C. under a pressureof 50 bar of hydrogen.

After precipitating from methanol, 1.75 g of SBM are obtained, which SBMis 30% hydrogenated (i.e. a degree of hydrogenation 60% lower than thatobtained with bmimPF₆) and has a rhodium content of 15 ppm.

Example 9

If the ethylbenzene in Example 1 is replaced with the same volume oftetrahydrofuran, a similar result is obtained.

Example 10

The hydrogenation is carried out exactly as in Example 1 but using theSBM-2 triblock copolymer.

The hydrogenated copolymer with a degree of hydrogenation of 63% isobtained. Its DSC analysis shows a melting point at 36° C. (accuracy:±2° C.), whereas the starting material (SBM-2) is not crystalline.

Example 11

The hydrogenation is carried out exactly as in Example 1 but using theSMB-3 triblock copolymer.

A hydrogenated copolymer with a degree of hydrogenation of 70% isobtained. Its DSC analysis shows a melting point at 45° C. (accuracy:±2° C.), whereas the starting material (SBM-3) is not crystalline.

Example 12

The hydrogenation is carried out exactly as in Example 1 but replacingthe SBM-1 triblock copolymer with the SBS copolymer.

A hydrogenated copolymer with a degree of hydrogenation of 85% isobtained. Its DSC analysis shows a melting point at 73° C. (accuracy:±2° C.), whereas the starting SBS is not crystalline.

Although the invention has been described in conjunction with specificembodiments, it is evident that many alternatives and variations will beapparent to those skilled in the art in light of the foregoingdescription. Accordingly, the invention is intended to embrace all ofthe alternatives and variations that fall within the spirit and scope ofthe appended claims. The foregoing references are hereby incorporated byreference.

1. Process comprising the selective hydrogenation of the olefinic doublebonds of a block copolymer, at least one block of which comprises one ormore olefinic double bonds, using a catalyst based on a metal from GroupVIII in a medium comprising an organic solvent for the copolymer and anionic liquid as solvent for the catalyst, a water-immiscible ionicliquid is used.
 2. Process according to claim 1, wherein the anion ofthe ionic liquid is the hexafluorophosphate anion.
 3. Process accordingto claim 1, wherein the cation of the ionic liquid is a quaternaryammonium, aromatic ammonium, quaternary phosphonium or ternarysulphonium cation.
 4. Process according to claim 3, wherein the cationof the ionic liquid is an imidazolium cation of formula:

in which X¹ and X_(3,) which are identical or different, are C₁–C₄ alkylradicals and X² is a hydrogen atom or a methyl radical.
 5. Processaccording to claim 4, wherein the cation of the ionic liquid is the1-butyl-3-methyl-imidazolium (bmim⁺) or 1-ethyl-3-methylimidazolium(enim⁺) cation.
 6. Process according to claim 1, wherein the organicsolvent for the copolymer is an aromatic solvent.
 7. Process accordingto claim 1, wherein the catalyst is based on rhodium, on ruthenium or onpalladium.
 8. Process according to claim 1, wherein the ratio of thevolume of ionic liquid to the volume of organic solvent is between 0.05and
 5. 9. Process according to claim 1, wherein use is made of 0.01 to 5mol of catalyst per 100 mol of olefinic double bonds to be hydrogenated.10. Process according to claim 1, wherein the hydrogenation is carriedout at a temperature of between 20 and 150° C.
 11. Process according toclaim 1, wherein the hydrogenation is carried out at a hydrogen pressureof between 1 and 100 bar.
 12. Process according to claim 1, wherein whenthe reaction mixture does not separate by settling, the hydrogenatedcopolymer is precipitated by introducing the reaction mixture, broughtto a temperature of between 20 and 80° C., into a non-solvent for thehydrogenated copolymer, this non-solvent being employed in an amountranging from 1 to 20 times the volume of the organic solvent. 13.Process according to claim 12, wherein the non-solvent is employed in anamount ranging from 2 to 10 times the volume of the organic solvent. 14.Process according to claim 12, wherein the non-solvent is an alcohol.15. Process according to claim 12, wherein the temperature of thenon-solvent, before the introduction of the reaction mixture, is between0 and 60° C.
 16. Process according to claim 1, hydrogenating apoly(styrene)-b-poly(butadiene)-b-poly(methyl methacrylate) blockcopolymer, the poly(butadiene) block of which predominantly possesses a1,4-microstructure.
 17. Process according to claim 4, wherein the cationis a 1,3-dialkylimidazolium cation.
 18. Process according to claim 7,wherein the catalyst is selected from the group consisting ofRhCl(PPh₃)₃, Rh(nbd)(PPh₃)₂ ⁺PF₆ ⁻, RuCl₂(PPh₃)₃ and PdCl₂(PPh₃)₂. 19.Process according to claim 8, wherein the ratio is between 0.1 and 1.20. Process according to claim 9, wherein use is made of 0.02 to 2 mol.of the catalyst per 100 mol. of olefinic double bonds to behydrogenated.
 21. Process according to claim 10, wherein hydrogenationis carried out at a temperature of between 50 and 125° C.
 22. Processaccording to claim 11, wherein hydrogenation is carried out at ahydrogen pressure of between 20 and 60 bar.
 23. Process according toclaim 12, wherein the reaction mixture, prior to the introductionthereof into the non-solvent, is brought to a temperature of between 20and 60° C.
 24. Process according to claim 13, wherein the amount of thenon-solvent is from 5 to 10 times the volume of organic solvent. 25.Process according to claim 15, wherein the temperature of thenon-solvent, before the introduction of the reaction mixture, is between0 and 40° C.